The invention relates to fluid flow machines in general, especially to centrifugal pumps, and more particularly to improvements in suction casings (called elbow casings) of fluid flow machines.
Many heretofore known elbow casings, wherein a shaft extends through a hole and a passage is provided for the flow of fluid medium substantially radially of and toward the shaft, are castings which are designed for ideal flow conditions. It has been found that such situations do not develop too often in actual practice when a centrifugal pump is associated or series or otherwise connected with (especially installed downstream of) numerous fluid flow controlling and/or guiding components including valves, gates, compensators, elbows and/or others. In many instances, such components can exert an adverse influence upon the profile of the flow in the pipeline and at the inlet to the pump. Since the maker of pumps is often not informed of the nature and/or number of components which are to be installed upstream of the pump, it happens again and again that the cross-sectional area of the flow path ahead of the pump, the profile of the flow and the passage in the elbow casing of the pump are out of harmony. This can enhance the development of noise and/or cause a reduction of the efficiency of the pump and, due to unsatisfactory flow of incoming fluid, can lead to a less satisfactory NPSH (net positive suction head) and to cavitation with resulting damage to important parts of the pump.